Commodore PET Series Machine Hub
PET 2001, 3000, 4000 & 8000 series workbench reference — 9″ & 12″ CRT safety & "Killer Poke" warning, "Garbage Screen" diagnostics, 6540/6550 & 2114/4116 memory repair, and IEEE-488 bus pinouts.
9″ / 12″ CRT High-Voltage Safety & The Infamous PET "Killer Poke" Warning!
Unlike ordinary monitors that include an internal horizontal oscillator (`555` / `TDA1180`), the built-in 9-inch and 12-inch monochrome CRTs in the Commodore PET are direct-drive monitors: the horizontal output transistor (`BU406D` / `2SD234`) and flyback transformer are driven directly by the TTL `HORIZ DRIVE` pulse (`J7 Pin 5`) from the PET motherboard! This creates two critical hazards: (1) Inside the monitor housing sits ~10 kV–13 kV of lethal anode voltage (plus un-isolated mains or +18 V/+55 V B+ rails), and (2) running early PET 2001 `POKE 59458,62` fast-print software on a 12-inch CRTC-equipped 4000/8000 ("Fat-40" / 8032) alters the horizontal drive timing and can physically overheat and destroy the CRT flyback transformer and horizontal output transistor!
1 What Is the PET "Killer Poke"?
- How It Started on Non-CRTC PETs (2001 / 3032 / Early 4032): On early 9″ PETs without a 6845 CRTC chip, VIA `CB2` (`59458` decimal, `$E842` bit 5) controlled a blanking wait-state line. Programmers discovered that executing
POKE 59458,PEEK(59458) OR 32(or `POKE 59458,62`) disabled vertical-blank wait states and sped up screen printing by 4×! - Why It Kills 12″ CRTC PETs (Fat-40 4032 & 8032): When Commodore redesigned the 12″ 4032 ("Fat-40") and 8032 around the MC6845 CRTC, they repurposed that exact VIA pin (`59458` bit 5) to control character line height / vertical timing! On early 12″ analog monitor boards without protection diodes, executing `POKE 59458,62` collapses vertical sweep or shifts horizontal drive duty cycle, burning out resistor `R752`, the `7812`/`7818` regulator, or the flyback stage!
- Rule: Never run `POKE 59458,62` on any PET that plays a piezo "chirp-chirp-chirp" beep on power-up (all chirping PETs have a 6845 CRTC chip!).
2 CRT Anode Discharge & Recapping
- Unplug mains power and prop open the heavy hinged steel top hood using its built-in support rod (just like a car bonnet!).
- To work on the 9″ (white/green P4/P31) or 12″ (green P31) CRT board, clip a heavy jumper wire to the bare metal CRT chassis frame and slide an insulated flathead screwdriver under the rubber anode suction cup until it clicks against the spring clip (hold 5 seconds, repeat after 1 minute).
- Monitor Board Recapping Priorities:
- Replace the non-polarised (Bipolar) horizontal coupling capacitor (`4.7 μF` or `10 μF 50V NP`) — when it dries out, the raster shrinks horizontally or loses linearity!
- Replace all electrolytic caps around the vertical deflection IC/transistors (`10 μF`–`1000 μF 35V`) to prevent vertical collapse (a bright horizontal line across the middle of the screen).
- Reflow cracked solder joints on the 7-pin `J7` video header and flyback transformer pins!
3 Geometry, Width & Focus Controls
| Control | Location & Adjustment Tip |
|---|---|
| BRIGHTNESS | Rear of monitor shell (or sub-pot on CRT PCB). Set so black background raster is just invisible. |
| V-HEIGHT & V-LIN | Trimpots on CRT PCB. Adjusts vertical height and top-vs-bottom character row symmetry. |
| H-WIDTH Coil | Hex ferrite slug on CRT PCB. Use a plastic hex alignment tool ONLY (a metal Allen key cracks the ferrite slug!). |
| FOCUS | Pot on CRT neck board or flyback. Adjusts character sharpness across all 40/80 columns. |
PET Hardware Generations & Motherboard Selector
Compare the four distinct motherboard architectures spanning the 1977 PET 2001 through the 80-column CBM 8032 / 8096 / SuperPET.
Original PET 2001-4 & 2001-8 1977–1978 • ASSY 320008 • Chiclet Keyboard & Built-in Datasette
Designed by Chuck Peddle and Bill Seiler in 1977 as the world's first all-in-one personal computer (forming the "1977 Trinity" alongside the Apple II and TRS-80 Model I). Identifiable by its folded sheet-steel case, 9″ blue-or-black bezel CRT, built-in Sanyo/Commodore cassette deck on the left, and small calculator-style "chiclet" keyboard on the right. Internally, the original `ASSY 320008` motherboard uses 100% Static RAM — assembled in four permutations of proprietary MOS `6540`/`6550` or industry-standard `2316B`/`2114` chips!
Key ICs & Architecture (`ASSY 320008`)
- CPU (`C4`): MOS 6502 @ 1.00 MHz
- PIA #1 (`G8` — `$E810`): MOS 6520 — Keyboard row scanner (`PA0–PA3` via 74LS145), Cassette #1 Sense, and Vertical Blank (`SYNC`) input
- PIA #2 (`B8` — `$E820`): MOS 6520 — 8-bit bi-directional IEEE-488 data bus (`PA0–PA7` In, `PB0–PB7` Out) and `NDAC`/`DAV` handshakes
- VIA (`A5` — `$E840`): MOS 6522 — User Port (`PA0–PA7`), Cassette motor control, `CB2` audio/shift-register output, and IEEE-488 `NRFD`/`ATN`
- Video Timing: Discrete 74LS TTL counters (NO 6845 CRTC chip!) reading 1 KB of dedicated Video SRAM (`$8000–$83FF` at `C3` & `C4`)
- Four Onboard 7805 / LM340T5 Regulators (`VR1–VR4`): Instead of one large 5 V supply, the 2001 board distributes heat across four separate TO-220 7805 regulators bolted to heatsinks right on the PCB!
The 4 Factory Combinations of 2001 RAM (`6550` vs `2114`) & ROM (`6540` vs `2316B`)
Check the white IC sockets on your `ASSY 320008` board — Commodore produced four versions of this board depending on whether it used 28-pin MOS `6540` ROMs / 22-pin MOS `6550` SRAMs or 24-pin `2316B` ROMs / 18-pin `2114` SRAMs:
| Board Variant | ROM Sockets (`H1–H7`) | SRAM Sockets (`I1–J8` & Video `C3/C4`) |
|---|---|---|
| Type A (Earliest 1977) | 7× MOS 6540 (28-pin, 2 KB clocked ROM) | 16× MOS 6550 (22-pin, 1K×4 clocked SRAM) |
| Type B | 7× MOS 6540 (28-pin) | 16× 2114 (18-pin, 1K×4 standard SRAM) |
| Type C | 7× 2316B (24-pin, 2 KB) | 16× MOS 6550 (22-pin) |
| Type D (Easiest to Service) | 7× 2316B (24-pin) | 16× 2114 (18-pin standard SRAM) |
Never Discard a Working `6540` ROM or `6550` SRAM! The 28-pin MOS `6540` and 22-pin MOS `6550` were only ever used in the 1977 PET 2001 and fail frequently. If any fail, plug in a modern 6540-to-2716 ROM adapter or 6550-to-2114/6116 SRAM adapter (or a single-socket ROMulan / PETvet / 6502 RAM+ROM replacement board under the CPU)!
PET 2001-N / CBM 3008 / 3016 / 3032 1979–1980 • ASSY 320351 • Full-Travel Keyboard & 4116 DRAM
In 1979 Commodore removed the internal cassette deck to make room for a full-size mechanical calculator-layout (or business-layout `B`) keyboard, upgraded the firmware to BASIC 2.0 (`### COMMODORE BASIC ###`), and replaced the hot static RAM array with sixteen `4116` (16K×1) dynamic RAMs (`32KB`) plus standard 24-pin `2332` (4 KB) ROMs! Sold as the `2001-16N`/`2001-32N` in North America and the `CBM 3016`/`3032` in Europe.
Key Architectural Highlights (`ASSY 320351`)
- No 6845 CRTC Chip (Hardware 40×25 Video): Video timing is still generated by discrete 74LS counters reading 2× `2114` Video SRAMs (`UF7` & `UF8`, `$8000–$83FF`) — meaning the video display starts up instantly even if the 6502 CPU or ROMs are completely dead!
- Main RAM (`UI2–UI9` & `UJ2–UJ9`): 8× or 16× 4116 DRAMs (requiring +5 V, +12 V, and −5 V!).
- 24-Pin 4KB ROM Sockets (`UD6–UD9` + `UF10` Char ROM): Uses standard 24-pin `2332` (4 KB) mask ROMs — meaning industry-standard `2532` UV EPROMs drop straight in with zero adapters!
Why `ASSY 320351` ("Dynamic PET") Is the Best Game Machine
Because `ASSY 320351` has a full-travel keyboard, up to 32 KB of RAM, and retains the original non-CRTC 9″ video hardware (and doesn't suffer from the CRTC "Killer Poke"), it runs nearly 100% of classic 40-column PET games (Space Invaders, Petgalaga, Microchess, Dungeon). Many owners install a 3-way ROM switcher to toggle between BASIC 1.0, BASIC 2.0, and BASIC 4.0!
CBM 4016 / 4032 ("Thin-40" vs. "Fat-40" Universal CRTC Board) 1980–1982 • ASSY 8032080 • BASIC 4.0
Introduced Commodore BASIC 4.0 (`*** COMMODORE BASIC 4.0 ***`) with built-in disk commands (`DIRECTORY`, `DLOAD`, `DSAVE`, `HEADER`, `COPY`), a hardware piezo "chirp" speaker on `CB2`, and the Motorola MC6845 / MOS 6545 CRTC video controller! Early "Thin-40" 4032s used a 9″ CRT, while later "Fat-40" 4032s used the wider 12″ green-phosphor CRT cabinet and the Universal Dynamic Motherboard (`ASSY 8032080` / `8032089`) (which is actually an 8032 motherboard configured via jumpers for 40 columns!).
Crucial Diagnostic Difference on CRTC PETs (4032 / 8032)
- No "Garbage Screen" If the CPU/ROM Fails Before Initialising the 6845 CRTC! Unlike the 2001/3032 (where discrete TTL counters always scan the screen), on a CRTC-based 4032 or 8032 the 6845 CRTC (`UB13`) outputs ZERO Horizontal or Vertical drive pulses until the 6502 CPU executes the Editor ROM (`$E000`) and writes the 18 CRTC timing registers!
- Listen for the Power-On Piezo Chirp (`"Bleep-bleep-bleep"`): The Editor ROM (`UD7`) plays the 3-tone piezo chirp immediately after programming the 6845 CRTC registers!
- Chirp Heard + Black Screen: CPU, Kernal (`$F000`), Editor (`$E000`), and CRTC init succeeded! Check the 12″ CRT monitor, J7 video cable, or 74LS video output gates.
- NO Chirp + Black Screen: CPU never reached the Editor ROM! Check power rails, 6502 reset/clock, Kernal ROM (`UD6`), Editor ROM (`UD7`), or shorted low 4116 DRAM!
Converting a Universal Board (`8032080`) Between 40 and 80 Columns
The late "Fat-40" 4032 and the 8032 share the exact same `ASSY 8032080` PCB — the 4032 simply leaves the second bank of two `2114` Odd-Column Video SRAMs (`UC6`/`UC7`) unpopulated, sets jumpers for 1 KB VRAM instead of 2 KB, and fits the 40-column Editor ROM (`901498-01` / `901499-01`)!
CBM 8032 / 8096 / 8296 & SuperPET (SP9000) 1980–1984 • 80×25 Green CRT • Business Keyboard
Commodore's flagship 80-column office and university computers. To double horizontal bandwidth from 40 to 80 characters per line without requiring double-speed SRAMs, the 8032 splits its 2 KB of Video RAM (`$8000–$87FF`) into two parallel 1 KB banks fetched simultaneously on every character clock: Even Columns (0, 2, 4…) live in `UC4` & `UC5` (`2114`) and Odd Columns (1, 3, 5…) live in `UC6` & `UC7` (`2114`)!
8000 Series Variants
- CBM 8032 (`ASSY 8032080`): 32 KB Main RAM (`16× 4116`) + 2 KB Video RAM (`4× 2114`) + BASIC 4.0 + Business Keyboard (`B`).
- CBM 8096: An 8032 factory-fitted with the 64 KB Memory Expansion Daughterboard (`ASSY 8032096`) (populated with `8× 4164` DRAMs) sitting over the 6502 socket (`96KB` total RAM for LOS-96 / WordPro!).
- CBM 8296 / 8296-D: Sleek rounded cream Porsche-styled case with 128 KB onboard RAM (`16× 4164`), PLA logic (`UE5`/`UE6`), and optional internal dual `8250LP` floppy drives.
- SuperPET (`MMF 9000`): Developed with the University of Waterloo — adds a secondary motherboard with a Motorola MC6809 CPU, 64 KB banked RAM, RS-232 serial port, and three side toggle switches (`6502` / `6809` / `PROG`) to run Waterloo APL, Pascal, Fortran, Cobol, and 6809 Macro Assembler!
8032 Even vs Odd Video RAM (`UC4–UC7`) Fault Decoder
| 2114 SRAM Chip | Columns & Bits Controlled | Visual Screen Symptom |
|---|---|---|
| UC4 (2114) | EVEN Columns (`0, 2, 4…`) Low Nibble (`ESD0–ESD3`) | Every 2nd character column (0, 2, 4…) shows wrong ASCII characters! |
| UC5 (2114) | EVEN Columns (`0, 2, 4…`) High Nibble (`ESD4–ESD7`) | Every 2nd character column (0, 2, 4…) is stuck in inverse video or wrong case! |
| UC6 (2114) | ODD Columns (`1, 3, 5…`) Low Nibble (`OSD0–OSD3`) | Every alternating odd column (1, 3, 5…) shows wrong characters! |
| UC7 (2114) | ODD Columns (`1, 3, 5…`) High Nibble (`OSD4–OSD7`) | Every alternating odd column (1, 3, 5…) is stuck in inverse video! |
Diagnostic Checklist: "Garbage Screen", White Sockets & IEEE-488
Step-by-step bench troubleshooting for the classic PET "Random Character Garbage Screen", notorious white IC sockets, and dead disk drives.
The Classic PET "Random Garbage Character Screen" Tree
On non-CRTC PETs (2001, 2001N, 30xx, early 40xx), powering on to a full screen of random, steady PETSCII characters (which never clears to `*** COMMODORE BASIC ***`) is the single most common fault!
- 1. What a Steady Garbage Screen Proves:
- Your 9″ CRT monitor, master crystal oscillator, video timing counters, Character ROM (`UF10` / `A2`), and `2114` / `6550` Video SRAMs (`$8000`) are WORKING!
- The screen is simply displaying the random power-on contents of Video SRAM because the 6502 CPU never executed the Kernal/Editor screen-clear loop!
- 2. Check the Notorious White IC Sockets First:
- Early 1977–1979 PETs used cheap white single-wipe plastic IC sockets that lose contact pressure and tarnish heavily. Gently rock/reseat the 6502 CPU, Kernal ROM (`$F000`), and Editor ROM (`$E000`) — or replace degraded white sockets with turned-pin / dual-wipe sockets!
- 3. Check 6502 Reset (`Pin 40`), Clock (`Pin 37`), and Ready (`Pin 2`):
- `Pin 40 (/RES)` is driven by a `555` timer (`NE555`) through an open-collector inverter. If the timing capacitor on the 555 is leaky, `/RES` stays stuck low (0 V)!
- 4. Check Zero-Page / Stack RAM (`$0000–$01FF`) & Kernal ROM (`$F000`):
- If the 6502 cannot read the reset vector (`$FFFC/$FFFD`) from the Kernal ROM (`H4`/`H7` on 2001; `UD9` on 3032) or cannot push a return address onto the 6502 Stack in Low RAM (`I1`/`J1` on 2001; `UI2–UI9` 4116 DRAM on 3032), it halts on the garbage screen!
- Plug a Romulan PET RAM/ROM / Tynemouth PET Diagnostic board into the 40-pin 6502 CPU socket to bypass all onboard RAM and ROMs in 30 seconds!
IEEE-488 Bus Troubleshooting (`DEVICE NOT PRESENT` / Hanging `LOAD`)
PET boots fine, but `LOAD"$",8` or `DIRECTORY` hangs on `SEARCHING FOR $` or immediately prints `?DEVICE NOT PRESENT ERROR` with a 2031, 4040, 8050, or PETdisk MAX / SD2PET.
- Suspect #1 — The Three `MC3446N` / `MC3446AP` IEEE-488 Bus Transceivers (`UA7, UA8, UA9` / `B9, A9, A10`):
- Three 16-pin Motorola `MC3446` quad bus transceivers sit directly between the rear IEEE-488 edge connector and the internal `6520` PIA / `6522` VIA!
- Static electricity or hot-plugging an IEEE-488 drive cable frequently kills one channel inside an `MC3446`, holding `DAV`, `NRFD`, `NDAC`, `ATN`, or one data bit (`DIO1–DIO8`) stuck high or low.
- Quick BASIC IEEE-488 Loopback Self-Test (No Drive Connected!):
- With nothing plugged into the rear IEEE-488 port, run this 1-line check in BASIC to verify that PIA #2 (`59424` = Data In, `59426` = Data Out) and both data `MC3446` buffers can drive and read back all 8 data bits (`0` to `255`):
FOR I=0 TO 255:POKE 59426,I:IF PEEK(59424)<>I THEN PRINT "BAD BIT:";I XOR PEEK(59424) NEXT:POKE 59426,255
- If any bit fails, either the corresponding `MC3446` data transceiver (`UA7`/`UA8`) or `6520 PIA #2` (`UB16`/`G8`) is faulty!
- With nothing plugged into the rear IEEE-488 port, run this 1-line check in BASIC to verify that PIA #2 (`59424` = Data In, `59426` = Data Out) and both data `MC3446` buffers can drive and read back all 8 data bits (`0` to `255`):
Internal Linear Power Supply & J7 CRT Monitor Pinouts
Checking the PET's heavy internal transformer, multiple onboard +5V/+12V/−5V regulators, and the 7-pin `J7` motherboard-to-CRT video connector.
Internal PSU Transformer & Multi-Regulator Architecture
Located in the rear-left base of the cabinet sits a massive mains transformer and an external/chassis-mounted 23,000 μF 15 V computer-grade screw-terminal filter capacitor. Raw ~8–9 V DC (plus 16 V AC center-tapped on dynamic boards) enters the motherboard on connector `J8` (`J10`/`J11`), where multiple local TO-220 / TO-3 voltage regulators regulate each section of the board:
| Motherboard Family | Regulators on PCB | Target Voltage & Role |
|---|---|---|
| PET 2001 Static (`ASSY 320008`) |
4× `LM340T5` / `7805` (`VR1, VR2, VR3, VR4`) |
+5.00 V DC (±5%) on EACH of the 4 regulators! Each 7805 powers a separate quadrant of the 6550/2114 SRAM and 6540/2316 ROM array. If just one of the four 7805s fails, a quarter of your RAM/ROM dies! |
| Dynamic PETs (3032 / 4032 / 8032) |
2× `LM323K` / `7805` (+5V) 1× `7812` (+12V) 1× `7905` (−5V) |
• +5.0 V DC: CPU, ROMs, 2114 VRAM, 4116 Pin 9 (`V_CC`) • +12.0 V DC: 4116 DRAM Pin 8 (`V_DD`) • −5.0 V DC: 4116 DRAM Pin 1 (`V_BB` — if −5V is missing, all sixteen 4116 DRAMs will burn up!) |
Internal `J7` Motherboard-to-CRT Video Header 7-Pin Inline Molex (`0.156″`)
Carries separate TTL-level Video, Vertical Drive, and Horizontal Drive (plus raw AC power for the monitor on pins 6/7 on some models, or via a separate 2-pin/3-pin AC monitor power plug). You can also tap `J7` into an RGBtoHDMI (TTL board) or a 3-resistor composite mixer to test a PET motherboard on an external monitor without the internal CRT!
| J7 Pin | Signal | Level & Timing Notes |
|---|---|---|
| Pin 1 | VIDEO DATA (TTL Pixel Stream) | 5 V TTL (Active-low on 2001/3032/4032; check polarity jumper on universal boards) |
| Pin 2 | GND (0 V) | Video Return Ground |
| Pin 3 | VERT DRIVE (Vertical Sync) | 5 V TTL Vertical Drive (60 Hz on Non-CRTC & NTSC; 50/60 Hz on CRTC) |
| Pin 4 | GND (0 V) | Vertical Return Ground |
| Pin 5 | HORIZ DRIVE (Horizontal Sync) | 5 V TTL Horizontal Drive (15.625 kHz on 9″ Non-CRTC; ~20.0 kHz on 12″ CRTC 4032/8032!) |
| Pin 6 | KEYWAY (Empty Pin) | Polarising keyway slot |
| Pin 7 | GND (0 V) | Horizontal Return Ground |
15.6kHz (9″) vs 20kHz (12″ CRTC) Horizontal Scan Rate Warning: Notice that 12″ CRTC PETs (Fat-40 4032 and 8032) run their CRT at a 20 kHz horizontal scan rate (not standard 15.6 kHz TV rate)! An RGBtoHDMI captures both 15.6 kHz and 20 kHz PET video effortlessly.
IEEE-488 (`J1`), User Port (`J2`) & Datasette (`J3`/`J6`) Pinouts
Rear PCB card-edge connector pinouts (0.156″ pitch) for connecting disk drives, PETdisk MAX / SD2PET, and CB2 sound amplifiers.
`J1` — IEEE-488 (GPIB) Bus Edge Connector 2×12 (24-Contact) • Rear Left
Connects Commodore 2040, 3040, 4040, 8050, 8250, SFD-1001, and 2031 disk drives, 4022/8023 printers, and modern PETdisk MAX / SD2PET SD-card drives. Top row = `Pins 1–12` (Left-to-Right viewing rear of PET); Bottom row = `Letters A–N` (excluding G, I):
| Top Pin (1–12) | IEEE-488 Signal | Bottom Pin (A–N) | IEEE-488 Signal |
|---|---|---|---|
| 1 | DIO1 (Data Bit 0) | A | DIO5 (Data Bit 4) |
| 2 | DIO2 (Data Bit 1) | B | DIO6 (Data Bit 5) |
| 3 | DIO3 (Data Bit 2) | C | DIO7 (Data Bit 6) |
| 4 | DIO4 (Data Bit 3) | D | DIO8 (Data Bit 7) |
| 5 | /EOI (End Or Identify) | E | /REN (Remote Enable — GND) |
| 6 | /DAV (Data Valid) | F | GND (Logic Ground) |
| 7 | /NRFD (Not Ready For Data) | H | GND (/DAV Return) |
| 8 | /NDAC (No Data Accepted) | J | GND (/NRFD Return) |
| 9 | /IFC (Interface Clear / Reset) | K | GND (/NDAC Return) |
| 10 | /SRQ (Service Request) | L | GND (/IFC Return) |
| 11 | /ATN (Attention Mode) | M | GND (/ATN Return) |
| 12 | Chassis Shield GND | N | GND (/SRQ Return) |
`J2` — Parallel User Port & `CB2` Audio Out 2×12 Edge • Center
Driven by the 6522 VIA (`PA0–PA7` & `CA1/CB1/CB2`). See also our dedicated PET IEEE-488 (`J1`) Bus, PET `J7` 7-Pin Video Header, and Datasette (`J3`/`J6`) pinout pages. Because early PETs (2001/3032) have no internal speaker, all PET game sound is output as a pulse-width / square-wave stream on User Port Pin M (`CB2`)!
| Top Pin | Signal | Bottom Pin | Signal & Bench Role |
|---|---|---|---|
| 1 | GND (0 V) | A | GND (0 V) |
| 2 | TV Video Out | B | CA1 (Handshake Input) |
| 3 | /SRQ IN | C – L | PA0 – PA7 (8-Bit Parallel User I/O + Stupid PET Tricks Dual Joystick!) |
| 4 | /EOI | M | CB2 (PET SOUND OUTPUT!) |
| 5 | DIAG (Pull to GND for Monitor!) | N | GND (0 V Audio Return) |
| 12 | GND (0 V) | Note: Keyway slot between Pins 1/2 and 9/10. | |
2-Minute PET Sound Amplifier Mod: Wire User Port Pin M (`CB2`) through a `10 kΩ` resistor + `0.1 μF` capacitor in series to the input of any powered desktop speaker (with Pin N = GND) for instant PET game audio! Also note: grounding Top Pin 5 (`DIAG`) at power-on boots straight into the built-in TIM Machine Language Monitor (`B*`)!
`J3` (Rear) & `J6` (Internal) Datasette Ports (`2×6` Edge)
Identical to the C64 and VIC-20 Datasette connector (`Pin A/1 = GND`, `Pin B/2 = +5V`, `Pin C/3 = +6V Motor`, `Pin D/4 = Read`, `Pin E/5 = Write`, `Pin F/6 = Sense`). Uniquely, every PET has two independent tape ports (`Device 1` and `Device 2`)!
Chip & 2532 / 2716 EPROM Reference
Interactive IC Pinout Finder cards for every major chip in the PET plus BASIC 1.0 / 2.0 / 4.0 ROM part numbers and EPROM rules.
MOS 6502 CPU
1.00 MHz 8-bit microprocessor driving every PET from the 1977 2001 to the 8296.
View Pinout →MOS 6520 / 6821 PIA (×2)
Two 40-pin PIAs (`$E810` Keyboard/Tape/VBlank & `$E820` IEEE-488 Data Bus). Motorola `MC6821P` is a 100% drop-in substitute!
View Pinout →MOS 6522 VIA
Mapped at `$E840` — User Port, `CB2` Sound shift register, Cassette motor control, and IEEE-488 handshake lines.
View Pinout →MOS 6545 / MC6845 CRTC
Fitted to 12″ Fat-40 (4032) and 80-column (8032/8096/8296) PETs to generate programmable 20 kHz CRT timing.
View Pinout →2114 SRAM (1K×4)
Used for Video RAM across all PETs (`2× 2114` on 40-col; `4× 2114` on 80-col) and Main RAM on 2001 Type B/D boards.
View Pinout →4116 DRAM (16K×1)
Triple-rail (−5 V, +12 V, +5 V) dynamic RAM (`16× 4116` = 32 KB) on 2001N, 3032, 4032, and 8032 boards.
View Pinout →PET BASIC 2.0 & BASIC 4.0 ROM Map (`2332` / `2316B` → `2532` / `2716` EPROMs)
On all dynamic PET motherboards (`2001N`, `3032`, `4032`, `8032`), the 4 KB ROM sockets (`$B000`, `$C000`, `$D000`, `$F000`) use the 24-pin `2332` mask ROM pinout (where `Pin 21 = +5V` and `Pin 18 = A11`) — which means Texas Instruments `TMS2532` / `2532A` (4 KB) UV EPROMs are a 100% DIRECT DROP-IN with zero adapters, whereas the 2 KB Editor ROM (`$E000`) and Character ROM accept a standard `2716` (2 KB) EPROM directly!
| Address Range | Role | BASIC 2.0 Part # (3032) | BASIC 4.0 Part # (4032 / 8032) | Direct EPROM Drop-In |
|---|---|---|---|---|
$B000–$BFFF(Socket `UD9` / `UD12`) |
BASIC 4.0 Disk/Extra Commands (Empty on BASIC 2.0!) |
Empty Socket | 901465-23 (or `-19`) |
2532 (4 KB, 24-Pin) direct drop-in! (Or `2732` via a 2332-to-2732 adapter). |
$C000–$CFFF(Socket `UD8` / `UD11`) |
BASIC Interpreter Low | 901465-01 |
901465-20 |
2532 (4 KB, 24-Pin) direct drop-in! |
$D000–$DFFF(Socket `UD7` / `UD10`) |
BASIC Interpreter High | 901465-02 |
901465-21 |
2532 (4 KB, 24-Pin) direct drop-in! |
$E000–$E7FF(Socket `UD6` / `UD7`) |
Screen Editor & Keyboard + CRTC Init (`2KB`!) | 901447-24 (Normal Keybd)901474-01 (Business Keybd) |
901498-01 (40-Col CRTC 50Hz)901499-01 (40-Col CRTC 60Hz)901474-04 (80-Col 8032) |
2716 (2 KB, 24-Pin) is a 100% Direct Drop-In! (Best socket for PETTESTER V4 by Dave Roberts!). |
$F000–$FFFF(Socket `UD5` / `UD6`) |
Kernal OS & IEEE-488 | 901465-03 |
901465-22 |
2532 (4 KB, 24-Pin) direct drop-in! |
| Character Generator (Socket `UF10` / `UA3`) |
2 KB / 4 KB Font ROM | 901447-10 (`2KB`) |
901447-10 (`2KB`) |
2716 (2 KB, 24-Pin) direct drop-in! |
Ultimate Diagnostic Tool — Burning `PETTESTER V4` into a `2716` EPROM for the `$E000` Editor Socket: Because the `$E000` Editor ROM is almost always in a socket and accepts a standard `2716` EPROM, plugging a `2716` burned with Dave Roberts's `PETTESTER` (`Eudi's PET Tester`) into the Editor socket requires zero working RAM to run: it initializes the CRTC, tests Video SRAM, tests Zero-Page/Stack RAM, checksums all ROMs, scans the keyboard, and loops a complete March-C test on all 16K/32K of 4116 DRAM!
Resources & Further Reading
Blog posts, interactive bench tools, and essential Commodore PET schematics & communities.
Smiggy's Commodore Posts
Bench Tools & Machine Hubs
- IC Pinout Finder — 6502, 6520/6821, 6522, 6845, 2114, 4116 & more
- Recap & Repair Reference — capacitor replacement guide
- Ohm's Law Calculator
- C64 Machine Hub — Commodore 64 reference
- VIC-20 Machine Hub — Commodore VIC-20 reference
- C128 Machine Hub — C128, C128D & DCR reference
- SX-64 Machine Hub — Executive Portable C64 reference
- Amiga Machine Hub — A500/A600/A1200 reference
- Big-Box Amiga Hub — A1000, A2000, A3000 & A4000 reference
- Atari ST Hub — 520ST, 1040STFM & STE reference
- Atari 8-Bit Hub — 400/800, 800XL & 130XE reference
- Apple IIe Hub — Unenhanced, Enhanced & Platinum reference
- BBC Micro Hub — Model B, B+ & Master 128 reference
- Acorn Atom & Electron Hub — Atom & Electron reference
- ZX Spectrum Hub — 16K/48K & +2/+3 reference
- Sinclair QL Hub — 68008, Microdrive & ULA reference
- Dragon 32/64 Hub — Dragon 32 & 64 reference
- Oric-1 & Atmos Hub — Oric 6502A & ULA reference
- Amstrad CPC 464 Hub — CPC 464 & Datacorder reference
- Amstrad CPC 6128 Hub — 128K & 3″ disc reference
- MSX Machine Hub — MSX1, MSX2, MSX2+ & Turbo R reference
- Osborne 1 & Kaypro II Hub — CP/M luggable reference
- Plus/4 & C16 (TED) Hub — 264 series reference
- TRS-80 & CoCo Hub — Model I/III/4 & CoCo 1/2/3 reference
- TI-99/4A Machine Hub — 16-bit TMS9900 & PEB reference
External Commodore PET Resources
- Zimmers.net PET Schematics & ROMs — complete Commodore factory schematics and ROM images for every PET/CBM board
- Andre Fachat's PET Index — deep-dive architectural analysis of static, dynamic, CRTC, and 8296 PET boards
- PETTESTER V4 (GitHub) — Dave Roberts's essential `$E000` diagnostic ROM and manual
- PETdisk MAX (Bitfixer) — modern IEEE-488 SD card & Wi-Fi drive emulator for all Commodore PETs